In the aviation industry, business aircraft (e.g. “business jets”) are classified into several categories or classes of aircraft: very light business aircraft, light business aircraft, midsize business aircraft, etc. Commercially they are used to transport a small number of passengers (in general at most a few tens).
Whatever the class thereof, business aircraft have at least one door, in particular the cabin access door, comprising, on one surface oriented towards the inside of the aircraft in a closed position thereof, stairs having treads and risers. The access door opens and closes by pivoting around a substantially horizontal axis parallel to the centerline of the aircraft, meaning the fixed reference line corresponding to the longitudinal axis thereof.
The trend is to replace the opening/closing maneuver of the door currently done manually by an operator positioned inside the aircraft near the door by an automatic operation performed by a properly controlled motorized mechanism. In this context, the opening/closing operation of the door could be controlled without the operator having direct visibility of the door itself, for example from the cockpit of the aircraft by one of the cockpit crew members and not by a commercial crew member.
To avoid the risk of closure at the door when, for example, a person or an object is still located on the open door, specifications require the use of security devices with which to detect an abnormal load (for example around 30 pounds, or 13.6 kg) present on the door at the moment of initiating the door closure sequence and inhibiting it.
Such known safety devices operate by comparison of a threshold and a current value in an electric drive motor for the door which reflects the torque delivered by the motor. Exceeding the threshold indicates an abnormal force needed for starting the door closure sequence. In that case, it is concluded that a load is present on the door and the sequence is immediately interrupted. This type of device gives an indirect detection of the presence of a load.
With reference to the attached drawings, FIG. 1A schematically shows an example of system 1 for opening/closing an aircraft door integrated in the inner wall 2 of the aircraft. Similarly, FIG. 1B shows a system of the same type, but integrated into the door 3 of the aircraft. FIG. 1C is a functional diagram of the main elements of the control system 1.
Door 3 of the aircraft is a swinging door mobile around a swinging axis 21 substantially parallel to the longitudinal axis (centerline) of the aircraft. The door 3 has integrated boarding stairs 31 on the surface thereof turned towards the inside of the aircraft in closed position of the door. The stairs 31 comprise respectively associated treads 32 and risers 33.
The door 3 can swing around the axis 21 from an open position to a closed position, or vice versa, because of a motorized mechanism. In closed position, the door 3 blocks the opening which is provided in the inner wall 2 for boarding, meaning for access on board the aircraft. In completely open position, the stairs 31 in fact allow access onboard the aircraft by the users (e.g. crewmembers, passengers, etc.) from the airport tarmac 300.
The door opening/closing system 1 includes an electric box 100 for opening/closing the door 3. In the example shown, the box 100 contains a pulley 101 driving the cable 103 for maneuvering the door 3 of the aircraft.
In the case from FIG. 1A, the box 100 is placed in the inner wall 2. The cable 103 is coupled to the door 3 by passing for example over a guide pulley 104 which is rigidly connected with the inner wall 2. Under the force of the traction exerted via the cable 103 by the pulley 101 when it is turned in a set direction, the door moves from the closed position to the open position. Inversely, when the pulley 101 turns in the other direction, the door moves from the open position to the closed position.
In the case from FIG. 1B, the box 100 is placed in the door 3. The cable 103 is then coupled to the inner wall 2. Under the force of the traction exerted via the cable 103 by the pulley 101 when it is turned in a set direction, the door moves from the open position to the closed position. Inversely, when the pulley 101 turns in the other direction, the door moves from the closed position to the open position.
In the embodiments described above, the mechanical coupling between the door 3 and the electric box 100 is done by a pulley 101 and a cable 103. Other embodiments can of course be provided for coupling the mechanical rotational movement of the door 3 to the control box 100.
With reference to the functional diagram from FIG. 1C, whatever the system architecture, i.e. whether it incorporates the inner wall 2 as shown in FIG. 1A or it incorporates the door 3 as shown in FIG. 1B, the pulley 101 is moved by a motorized mechanism 102. The mechanism 102 is driven by a driving unit 105. The unit 105 is paired with a unit 106 for monitoring the current in the motorized mechanism 102. On command from the operator, the driving unit 105 drives the motorized mechanism 102 which controls the pulley 101 for winding/unwinding of the cable 103. The winding of the cable 103 leads to the closure of the door. Inversely, the unwinding of the cable leads to the opening of the door.
During closure of the door, the current consumption in the motorized mechanism 102 reflects the torque that has to be generated in order to close the door. In case of exceeding a set current threshold, the monitoring unit 106 generates a signal for detection of an abnormal load on the door which is sent to the driving unit 105. In response to this detection signal, the driving unit stops the closure of the door, and could possibly command the reopening thereof, via commands that it applies to the motorized mechanism 102.
However the value of the load to be detected is small compared to the mass of the door to be moved. Additionally, it is small compared to the equivalent force that the wind, for example, can produce on the door. Finally, the mass of the door can be different from one aircraft to another, even of identical brands and models, depending on the selected options.
In other words, many factors can impact the value of the current in the motorized mechanism 102, independent of the presence or not of a load on the door 3. These factors vary from the condition of the system itself (e.g. mechanical friction) to meteorological conditions (e.g. wind, temperature) by way of the power supply network voltage (in principle equal to 28 V in the aircraft, but subject to inevitable variations depending in particular on conditions of use).
All these reasons can lead to false alarms or, inversely, to the failure to detect the presence of people or objects on the door, according to the adjustments of the system. Additionally, not only is the definition of the initial parameters difficult, but additionally the inevitable drifts over time can generate significant false alarm rates.